fix: add discord mention context history

docs/configuration.md

@@ -178,7 +178,8 @@ Configure the Discord bot by setting the bot token and optional gating:
       users: ["987654321098765432"]        // optional user allowlist (ids)
     },
     requireMention: true,                   // require @bot mentions in guilds
-    mediaMaxMb: 8                           // clamp inbound media size
+    mediaMaxMb: 8,                          // clamp inbound media size
+    historyLimit: 20                        // include last N guild messages as context
   }
 }
 ```